In recent years, an interface apparatus which is a combination of a projector and a camera has been developed. In the interface apparatus, the projector projects an image to a projection surface, such as a table or a wall, and the camera detects the position or movement of the hand or finger of an operator for the projected image. In this way, an interactive operation is achieved. NPL 1 discloses an interface apparatus which is called the Everywhere Displays Projector (hereinafter, referred to as an ED projector) using a projector and a camera. The ED projector disclosed in NPL 1 can project an appropriate image according to the state of a projection surface and detect the operation of the operator for the projected image.
A modulation method of a projector includes an intensity modulation method and a phase modulation method. A general interface system uses an intensity-modulation-type projector. In the intensity modulation type, the intensity of illumination light is changed for each pixel of a modulation element and pixels on a screen are in one-to-one correspondence with pixels on the modulation element. Therefore, even when black is displayed, light with certain intensity is output, which results in unnecessary power consumption. In addition, in the intensity modulation type, as the distance between the projector and the screen increases, projection light is enlarged at a certain magnification. In this case, the size of an image projected to the screen increases as the distance increases and projection light is darkened in inverse proportion to the square of the distance. Therefore, it is necessary to increase the size of the apparatus to increase the brightness of a light source of the project, in order to obtain a clear image in a dark place in which contrast is significantly low.
In contrast, in the phase modulation type, the pixels on the screen are not in one-to-one correspondence with the pixels on the modulation element and the pixels on the modulation element are associated with all of the pixels on the screen. In the phase modulation type, since light is focused on a necessary portion, no light is projected to a portion on the screen in which black is displayed and power is not unnecessarily consumed. Therefore, in the phase modulation type, power efficiency is higher than that in the intensity modulation type. In addition, the phase modulation type can be designed such that an image is not darkened even when the distance between the projector and the screen increases. In addition, in the phase modulation type, since the pixels on the screen are not in one-to-one correspondence with the pixels on the modulation element, a defective pixel of the modulation element does not become a defect on the screen.
When a phase-modulation-type projector is used to project an image with a substantially small projection area, such as a line image or characters, it is possible to achieve a wearable interface system with a small size and low power consumption. PTL 1 discloses a projection display device including a phase modulation means.
In an interface system that projects, for example, a line image or characters, it is preferable that classifications be displayed in different colors in order to easily distinguish projection images. Therefore, it is necessary to project multicolor light. As a system for displaying multiple colors using a projector, there is a three-chip system or a time division system. PTL 2 discloses a phase-modulation-type projector that displays multiple colors using the three-chip system. PTL 3 discloses a phase-modulation-type projector that displays multiple colors using a combination of a three-chip system and a time division system.